Metallocenes make polymers with uniform, narrow molecular weight distribution (MWD), high comonomer content, relatively even comonomer distribution and an enormously wide choice of comonomers, compared to multi-site Ziegler-Natta catalysts.
It is known that a variety of metallocene-made thermoplastic polymer have excellent properties, but lack good melt processability. Higher toughness and good melt strength are attributes of higher molecular weight grades, and as a result, melt processing machine outputs tend to be inversely related to the desirable qualities of toughness needed for durable goods, etc. and melt strength needed for film, thermoforming, blow molding, injection molding, etc.
European Patent Application No. 455,481, having Shell Oil Company as the applicant, discloses the use of a high melt index poly-1-butene to thermoplastic polymers made by conventional Ziegler-Natta catalysts to improve the processability of the thermoplastic polymers made by conventional Ziegler-Natta catalysts.
However, there remains a need for improving the processability of thermoplastics made by metallocene catalysts, which differ from the conventional Ziegler-Natta catalyst made thermoplastics.
Moreover, it has been found that the addition of poly-1-butene to low density polyethylene does not improve the processability of the low density polyethylene.
Therefore, there remains a need for a commercial process which will improve the processability of metallocene-made thermoplastic polymers, especially metallocene-made ethylene-.alpha.-olefin copolymers, particularly metallocene-made low density ethylene-.alpha.-olefin copolymers.